The barn owl (Tyto alba) relies heavily on its ability to localize sounds in order to survive. Owls are able to locate prey solely by the sounds these prey produce. Their behavioral capabilities are reflected in their central nervous system. Areas of the brain responsible for processing auditory information are highly developed in size and capabilities. This makes the barn owl an excellent animal in which to study how the brain processes and localizes sound. Although the basic principles of sound localization are starting to be understood, the datails of how the brain accomplishes this task are largely unknown. This research proposal is aimed at discovering how the brain processes one of the important cues used for sound localization--interaural time (phase) differences. The project relies on intracellular techniques to demonstrate directly the synaptic events that enable owls to compare time differences with a resolution of several microseconds. The activity of single neurons will be recorded with intracellular microelectrodes in response to dichotic stimuli. The activity will be analyzed to discover how time differences are compared. The synaptic basis of interaural time difference comparison will be measured from the first site of comparison in the brainstem, to the extremely sensitive neurons of the midbrain. The morphology and location of specific neurons will be obtained by injecting fluorescent dye into the cells. This provides the ability to relate structure to function. The findings of this proposal can be applied to animals other than barn owls. Other vertebrates, including primates and humans, also localize sounds accurately. Research on these many systems have shown strong parallels between the barn owl auditory system and those of higher vertebrates. Thus, the results of the proposed study should be applicable to the understanding of how primate, and even human brains process auditory information. Such basic knowledge is of utmost importance for understanding how the normal brain functions, and ultimately, how defects might be corrected to restore normal functions.